IMX Seminar Series - Co-continuous Nanostructures in Charged Polymer Materials

Nanostructured materials with co-continuous structures, in which each discrete domain is independently interconnected, can simultaneously optimize “orthogonal” properties such as ion transport and mechanical strength. Potential applications include porous membranes, fuel cells, and rechargeable metal batteries. Block polymers have been exploited as templating agents to access such morphologies, for example via ordered periodic phases such as the double gyroid, or by polymerization-induced microphase separation. In such cases the conducting domains are typically ≤ 20 nm in size, which can compromise both mobility and strength. An alternate route involves blending an A–B diblock copolymer with the constituent A and B homopolymers, leading to a disordered bicontinuous microemulsion (BmE) state. We have shown that charge-free ternary A–B/A/B polymer blends universally self-assemble into the thermodynamically stable BmE phase, albeit with carefully designed molecular weights and compositions. The BmE displays globally disordered but locally correlated domains, with tunable characteristic length scales in the range of ca. 20–100 nm, well beyond the domain sizes typically associated with pure diblocks. The interesting question that arises is whether this phase can also be accessed in blends containing charge, where in general the intermolecular interactions are stronger and more long-ranged. We are exploring this issue in two cases: an A–B/A/B ternary system with added salt, and an A–B/A/B system in which one of the polymers is ionomeric.